<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>无标题文档</title>
<style type="text/css">
    #box { width:400px; height:30px; border:1px #666666 solid; padding:10px; overflow:hidden;}
    #box h5{ border:1px #666666 solid; height:30px; margin:0; padding:0;}
    #box p{  border:1px #666666 solid;}
    #box:hover { height:100px;}
</style>
</head>
 
<body>
 
<div id="box">
    <h5> + 标题</h5>
    <p>这里是内容，也可以用   #box:active { height:100px;}，这是鼠标按下的效果。</p>
</div>
 
</body>
</html>